This invention relates to a method and apparatus for medical diagnostic testing by using infrared radiation and, more particularly, to a method and apparatus for determining temperature differences between two or more sites on a body.
Differential skin surface temperature measurement has been useful for determining the ovulation time of women as well as other medical testing. A study by Shah et al, "Determination of Fertility Interval with Ovulation Time Estimation Using Differential Skin Surface Temperature Measurement," Fertility and Sterility, May 1984, indicates that the temperature of vascularity sensitive areas can be compared to vascularity insensitive areas to determine the time of ovulation. The vascularity sensitive area measured is the breast and the vascularity insensitive area is the sternum. Just before ovulation the temperature of the vascularity sensitive areas is greater than the vascularity insensitive areas.
Differential temperature measurement may also be useful for detecting soft tissue damage When tissue is inflamed the blood supply to it is increased. This increased blood supply increases the temperature of the tissue. Thus, by comparing the temperature of the damaged tissue to that of the undamaged tissue an injury can be detected. Such information may be useful, for example, in evaluation of so-called "whip-lash" injuries.
The present invention has particular application in determining temperature differences between two or more sites on a human body using infrared detectors. One advantage for using infrared detectors is that a measure of the surface temperature of a site on an object can be determined without contacting the object. However, if only one detector is used to measure the temperature at two or more sites, the probability of measurement inaccuracies due to moving the detector is great. On the other hand, if different detectors are used to measure the temperature at different sites, measuring inaccuracies due to drifts or tolerances between the different detectors is likely. An apparatus which can measure two or more sites on a human body or on other objects without these drawbacks is therefore desirable.
Infrared detectors measure the infrared radiation emitted by a surface. By analyzing the wavelength and intensity of the radiation, the surface temperature can be remotely determined. Detectors used in such systems, for example, pyroelectric infrared detectors, typically have a body of pyroelectric material and electrical output leads. A change in temperature of the pyroelectric material creates a change in polarization and current is produced only as the material experiences a temperature change. When it is at a constant temperature, no current is produced. When radiation is absorbed by the material, an electrical current flows in a circuit connected to the output leads thereby providing an indication of the radiation. Such detectors are not only exposed to the radiation emitted by the surface to be measured, but also to radiation emitted by themselves or their environment. Thus, the measuring accuracy of the system is reduced.
In one attempt to overcome this problem, two detector elements, connected in inverse parallel arrangement have been employed with one of the elements exposed to incident radiation while the other detector element is only exposed to internal or environmental radiation. In another attempt to overcome the accuracy problem, a system with a single detector element has been used together with a chopper which alternately exposes the detector to incident radiation and then to internal radiation only.
Prior patents pertaining to detecting temperatures of an object using radiation detectors include: U.S. Pat. No. 3,722,282 to Loy; U.S. Pat. No. 3,972,598 to Kunz; U.S. Pat. No. 4,268,752 to Herwig et al; U.S. Pat. No. 4,339,748 to Guscott et al; U.S. Pat. No. 4,442,357 to Baker et al; U.S. Pat. No. 4,514,630 to Takahashi; and U.S. Pat. No. 4,514,631 to Guscott.
U.S. Pat. No. 3,722,282 to Loy discloses the use of a modulator device which alternately switches the radiation transmitted to a detector between that emanating from a point in a scene and a reference beam which indicates the mean temperature of the scene. Loy requires a plurality of mirrors or lenses for focusing each beam of radiation onto a detector. U.S. Pat. No. 3,972,598 to Kunz discloses a multifaceted mirror structure which focuses light from a plurality of discrete points onto a single radiation detector. The Guscott and Takahashi patents are similar except that a dual mirror system is utilized for focusing radiation.
The patent to Herwig discloses an apparatus for focusing radiation beams from different directions onto a single detector in which a plurality of planar mirrors initially deflect incoming beams onto a concave mirror. The concave mirror reflects the beams onto a further deflecting mirror which directs the beams to a detector.
The patent to Baker et al discloses a differential radiation detection apparatus for determining the level of liquid in a container by measuring the temperature of the container above and below the level of the liquid. In that patent, the radiation from two points on the same object is reflected by a concave mirror to the detection apparatus. A disadvantage of this system is that the apparatus comprises a pair of thermal radiation detectors.
It is an object of this invention to provide a noncontact temperature sensing system and method for accurately determining a temperature differential on the surface of an object.
It is another object of the present invention to provide a temperature differential measurement system and method which is not prone to environmental effects.
It is still another object of the present invention to avoid temperature differential measuring inaccuracies originating from moving the measuring system.
It is still another object of the present invention to provide a method and apparatus for temperature differential measurement using the same radiation detector to measure the radiation from all points being measured to avoid drifts or tolerances between different detectors.